Means for focusing light sources in projectors



rPatented Nov. 6, 1928.(

oFF1cE.

j YEDWARD A. EvERETT, or NEW Yonx, N. Y.

HMEANSTOR FOCUSING IilGHT SOURCES IN PROJECTORS.

`Application mdiane 1s,

This invention relates to light projectors particularly of the type used in railway signals and ithas forits objects to provide a simple and effectivemeans for focusing the source of light'with relation to the lens of the pro-- jector whereby the maximum results are obtained from a weaksource of illumination. The objects of the invention and the method of applying thesame'will be more particu larly understood from the following specifica--V "tion and the accompanying drawings, in.

which,` Fig. 1,-`is\a sectional elevation ofa `railway signal lamp' embodying my invention, Fig. 2 is a cross-section of the focusing tube used inFig.' 1. Fig. 3 `is a detail used inv the construction ofthe focusing tube; Fig.

4 shows in section a modified construction of the sighting tube and Figs. 5 and 6 are details. Y i

In railway lightysignalswhich are used to project a beam of lightfor a distance along the track, itis commonfpractice to use concent1-ated filament electric bulbs fas the source of illumination for these signals., This filament has acomparatively low candle'povverY which is concentrated at a point and for proper operatingresultsv it4 is essential that this `'point be located in the exact focal point of the lens or reflector. `The present invention embodies `a sighting device for locating this `:fo`calpoint.A "i f L The bulb is provided'with an ordinary base supported on a stand and in view'of theffafct thatthe filamentV in commercial bulbs doesl not beara fixed relation to the base, the base 1 is supported on an adjustable stand similar to that shoivn in U.V S. Patent 1,535,218 issued April28,1925. i 1 Y.

It has been common practice `heretofore to locate the sourceof illumination by sighting y onthe axial line of the projecting lens and by sighting back from the lens-on its focal centre on anotheruline at right angles to the axial line ofthe lens.l Thisrequired two` sighting devices and required theoperator to change his position when using'eitlier device.

j Y The present invention embodies in one sighting device means for locating the source `of illumination on the axial line of the lens and means for accurately locatingV thissource at the focal centre of the'lens. These results are secured by a sighting tube sighting on the Y axial line of the projecting lens and by a sighting lens of short focus within the tube so that the definition of thel filament, when sight` f With the cross-,hairs or ed through'this `lens nitelylocating the filament,iwhich, by the construction, is the focal centre of theprojecting lens. This sighting lens has a magnifying effect on the filament so that the coils ofthe filament can be clearly seen When it is'in the focus of this lens. The operator thus locates the filament on the axial line of the projecting lens and locates it 'at the focal point of this lens with one sightingoperation therebysaving time and adding to the convenience in operating the device.

Referring to thedrawings, 1l is the lamp or 4projector housing which is provided with an opening at 12 having al suitable cover, not shown in thedrawings. The projecting lens 13 is centered in the housing at one end. The lamp bulb 14 is supported in the socket 1,6 carried by the bracket 17 which is adjustably supported on the screw stems 18 and 19 with" relation to the housing and the projecting' lens 13'. Thesource of illumination comprisesthe concentrated filament 15 of the bulb 14 WhichV should be located on the axialline bf-b ofthe lens 13 and onthe intersecting line a-a the intersecting pointlbeing the focal point of the lens 13. f

VThe rear of the housing 21 isyprovided with, a boss 22Which isdrilled on the line b-b tol receive the tube 23 the aperture of which is j designated c. VThis tube isprovided with a shoulder or collar at 33 engaging the boss and the inner end is threaded to receive the boss 24 of the reflector 25 Which` has an aperture aligning with the aperture c. A di sc26 with4 a peep hole closes the outer end of this aper- ,affords a meansof defii ture c and the innerend is closed by the douj ble convexlens 28and bythe glass screen 27`- indicated in Fig. 3. i

The axial line of thesighting lens on line b-b and itsfocal point is at the `centre mark 35 5 as ,i

the intersection of line a-a andline b-l-b. Thus'.I the fo;

cal centres of lenses l13 and 28 are the same.v point and these lenses are maintained in fixed relation to each other by the housing. It

will thus be seen that an object in the focus ofthe focusing lens 28 will be in the focus'of the projecting lens '13.

The .filament 15 may be sightedwhen it is lighted and it may be sighted in the day time when it is not lighted, by the light which is concentrated on theflament from lens 13. When the filament is lighted the screen 27 is smoked or rendered opaque to prevent irral (if) diation or glare so that the outline of the tilament can be distinguished in a sharp and magnified torni through the lens QS.

The position o'f the tilament is adjusted through the bracket 17 which raised and lowered and tilted by manipulating the adjusting screws as more particularlji described inthe patent abore referred to. The lament is located on the line bby the markings onthe screen 2T which may talge the form ot a central opening, concentric rings orother construction which enables` the centre of this disc to be readily determined. in con'tbination with the peep hole in disc 2G.

',lhe .filament is adjusted back and forth on line b-Ji towards and away from lensl 2S until the position ot its sharpest definition is found. This will be online awa. or the focal point ot lens '13. 1t will be noted that as the distance 'lrom 15 to lens 2S much less than the distance from to leus 13. the short focal range of lens 2S enables the filament to be located with great accurac.;v with an increased accuracy in its location with relation to the toc-.il point. of the projecting lens 13.

The lens Q8 is provided solely for focusing purposes and as conm'iercialljv sold has considerable rariation in its focal range. 1n order that commercial lenses may be used 'for this work. I provide an adjustable mounting for these lenses in the focusing tube 2?). Tl is comprises the slide 31 carrying the lens QS and the screen Q7 as indicated i'niFig. 4 and which maj' be adjustably positioned in the section ot increased diameter of the tube c at 3Q. The lens '2S can thus be located on a test ing stand in tube "23 and secured in position by anyv suitable means. so that when the sighting tubes so constructed are assembled in a housing with the collar 33 engaging the boss the focal point 15 determined by any sighting tube will be uniform.

The tilament as usually constructed. has two general forms. one is triangular as indicated at 15, Fig. 5 and the other is curved as indicated at 15', Fig. (i. In Fig. 5 the screen 2T has a. central aperture at 35 and the relation ot the triangular filament 15 can easilj7 be determined on the screen with respect to this aperture.

The screen 2T may be eliminated and corresponding eliects obtained trom the lens :58. In this ease the lens is smoked or obscured except for a ring around the outer edge, on

this smoked surface the image ot the lilament is clearly delined and its position with relation to the centre ot the lens is easily deter mined iii-practice Without a central marl; on the lens.

By this construction the optical centre of a projecting lens is determined by a single sighting device.

Haring thus described my iurention. l claim:

1. ln a focusing sight tor a projector, the combination, a housing having a projectingr lens, a lamp bulb haring a lilament and ay sighting' tube centered on the axial line ot said projectingl lens. said sighting tube comprising a screen with crosshairs tor locating said axial line and a sighting lens at one cud located in fixed relation to the 't'ocal point ot" said projecting lens and a sight atthe opposite end of said tube. the position of .said filament relative to said tof-al point being di terinined by the delinition of the lilan'ient on said screen when sigl'itcd through said tube.

Q. 1n a focusing sight tor a projector. the combination. a housing haring a ]u'ojectin;r lens. a lamp bulb having a lilament and a. sighting tube centered on the axial line ot said lens. said sighting tube having a screen and haring means for locatingr said axial line and having a sighting lens at one end located in fixed relation to the focal point ot said projecting lens and a sight at the opposite end ot said tube. the position ot said tilament relative to said lfocal point being determined by the definition ot the tilament on said screen when sighted through said tube.

3. 1n a focusing sight tor a projector. the combination. a housing having a projecting lens. a lamp bulb having a` filament and a sighting tube centered on the axial line of said lens, means in said tube for locating said axial line` said sighting tube haring a screen and a sighting lens adjustably positioned in said tube and located relative to the 'focal point ot said projecting lens and a sight in said tube. the position ot said filament relative to said 'focal point. beingl determined b v the definition of the filament. on said screen when sighted through said tube.

Signed at New Yorlc. in the couut \v ot New York and State ot' New York this 15th day of June. D. '1926. 

